Semiconductor elements such as transistors, integrated circuits (IC), and large scale integrations (LSI) are typically formed into a semiconductor device by encapsulating in a package such as a ceramic package or a plastic package. Ceramic packages have a superior resistance to high-temperature and high-humidity environments and a superior mechanical strength, due to the material thereof being highly resistant with respect to heat and humidity, and are capable of providing highly reliable encapsulation.
However, ceramic packages have problems such as being relatively expensive in material costs and being less suitable for mass production. Therefore, plastic packages, which use a resin for encapsulation, have been becoming predominant. As for the material for encapsulation in plastic packages, an epoxy resin composition has been suitably used due to its excellent heat resistance.
In the fields of automobiles, large home electronic appliances, industrial equipments and other industries, power devices such as transistors, diodes and thyristors are used as semiconductor devices for high-power regulation. These power devices produce a large amount of heat upon being subjected to a high voltage. Therefore, the power devices are provided with a lead frame that exhibits excellent heat radiation, such as a nickel-plated lead frame or an aluminum lead frame. However, these lead frames typically are less adhesive with respect to an encapsulating resin, as compared to a frame made of copper or an alloy such as 42 alloy. As a result, detachment from the encapsulating resin is likely to occur in a package. The detachment tends to decrease heat conductivity in the encapsulating resin and lower the reliability of the device. Against this background, development of a resin composition for encapsulation, which exhibits a favorable adhesion with respect to metallic materials that exhibit poor adhesion with respect to an encapsulating resin, has been demanded.
As an attempt to improve the adhesion of an epoxy resin composition for encapsulating a semiconductor device (hereinafter, also referred to as an “epoxy resin composition”) with respect to metallic materials, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-206016 proposes the use of a specific coupling agent having a thiol group. There are other proposed use of an agent, such as a silane coupling agent having an epoxy group or a silane coupling agent having a vinyl group (see, for example, Japanese Patent Application Laid-Open (JP-A) No. H03-119049).